1. Field of the Invention
The present invention relates to a paper feeder and a paper feeding method for taking paper for use in electro-photographic apparatus, printers and the like one by one surely and feeding them in a prescribed direction and an image forming apparatus.
2. Description of the Related Art
As a paper feeder used in an image forming apparatus, a paper feeder adopting a friction paper feeding system is now broadly put in practical use. This paper feeder takes out sheets of paper housed in paper supply cassettes according to the friction paper supply system using, for example, pickup rollers and taken out sheets of paper are separated one by one according to a friction separating system, that is, using a separation pad or a separation roller and sent out in an image forming direction.
In order to prevent adherence of sheets of paper in such a paper feeder, i.e., to prevent a plurality of adhered sheets from being supplied at one time, a device has been developed which prevents a supply of sheets of paper from adhering closely to each other by blowing an air stream into the end surface of sheets of paper in a paper supply cassette as disclosed in Japanese Patent Application No. 6-271127.
However, the above-mentioned conventional paper feeder is in a structure to blow an air stream between sheets of paper in the paper supply cassette and therefore, the air stream acts only on the leading edge of sheets of paper in the conveying direction and in the case of ordinary paper that are not so highly adhesive, supply of plural sheets is prevented but in the case of paper that are high adhesive, it becomes difficult to separate them because of high adhesion and take-out of sheets of paper is impeded. When an air stream is blown between sheets of paper in the paper supply cassette, a clearance is produced between a paper placed at the top position and a paper thereunder and a friction paper supply force of pickup roller acting on the top paper escapes. This is considered to be one of reasons for causing the above-mentioned trouble.
In recent years, when glossy paper coated with thin resin on both sides and extremely high adhesive is supplied to color copiers, the separation resisting force caused by the close adhesion generated on the overall surface of the glassy paper becomes stronger than the friction paper supply force of the pickup rollers made it difficult to separate sheets of paper and take out them. This phenomenon becomes remarkable especially in large size paper and actually, it becomes necessary to restrict size or kind of sheets of paper that are used in a paper feeder and functions of a paper feeder or an image forming apparatus is impaired and furthermore, reliability of an image forming apparatus requiring paper supply is also impaired.
Accordingly, when supplying sheets of paper that are extremely adhesive using the friction paper supply system, a certain paper supply is demanded regardless of size or kind of paper and it is desired to obtain a highly functional and reliable paper feeder, a paper feeding method and an image forming apparatus.